Modular, stackable, geothermal block system

ABSTRACT

A modular, stackable, geothermal block system for use as a subterranean or submarine heat exchanger in a geothermal energy system which provides a heating/cooling means to an external load. The stackable blocks, which can be filled with a fluid and/or material of generally high heat retention characteristics or precast in such material, contain one or more continuous passageways that extend from the top face of the block through the opposing face, through which a rigid structural heat exchange tube, fabricated from material of high thermal conductivity, is placed. The blocks are stacked one upon another and slidably mounted on the tube(s). Each tube contains a helically wound, thermal transfer tubing comprising one leg of a U-shape configured loop. Each stackable block can contain multiple paired passageways permitting more than one U-shape loop within the system.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

FEDERALLY SPONSORED RESEARCH

Not Applicable

SEQUENCE LISTING OF THE PROGRAM

Not Applicable

BACKGROUND OF THE INVENTION

The present invention relates to the transfer of thermal energy to andfrom subsurface and submarine environments to be utilized by anyheating/cooling system as well as any power generating system that couldexploit a temperature differential within a moving fluid.

Increasing awareness of the limited supply of fossil fuel reserves hasraised interest in alternative energy sources. Cost conscious consumershave expressed interest in solar power and wind power alternative energysources to supplement or replace conventional fossil-fuel based systems.Extensive research in these two fields and the fact that they are ableto supplement an existing electrical infrastructure has focused muchinterest in these two areas. However, the limitations ofweather-dependent solar and wind technologies are apparent. They are, ineffect, interruptible electrical power suppliers.

Geothermal, a third source of energy, can provide a much more reliablesource of alternative, renewable, non-polluting energy in a thermalform. The field of geothermal energy encompasses two substantiallydifferent disciplines. The first, involves the extraction of thermalenergy in the form of steam from below-ground sources near (volcanic)magmatic regions. Water pumped into overlying ground fissures quicklyabsorbs abundant quantities of heat and is transformed to steam which ischanneled to perform useful work. When the term “geothermal energy” isused, this method is often the one that is being described. However, thesame term is often used to describe the second discipline, which is alsothe subject of the present invention. All references to “geothermalenergy” in the description of the current invention will be based on thesecond discipline, which is described next. The second discipline is thetransfer of thermal energy to and from relatively shallow depths belowthe surface of the Earth using a liquid thermal transfer medium and attemperatures generally much lower than that of steam. This methodologyis often referred to as ground-source heat transfer, earth-coupled,geothermal heat pump and GeoExchange systems. A subsurface closed-loopsystem in which a finite amount of thermal transfer fluid isre-circulated to transfer heat between the earth and an above groundheating/cooling load is the most common ground source heat transfersystem in use today although there are other open-loop type systems.Underground loops commonly fabricated from copper or polyethylenetransport thermal transfer fluid, consisting of a refrigerant or aqueoussolution, respectively, to an indoor facility to accomplish heatingand/or cooling. Loops are placed in a predominantly vertical orhorizontal orientation. Installation of vertical loop systemsnecessitates the use of bulky, expensive drilling rigs to drill one ormore boreholes that are approximately four inches in diameter and two tofour hundred feet deep. Within this deep narrow borehole a U-shapelength of tubing is inserted to extract thermal energy from, or to putinto, the ground by circulating a thermal transfer fluid within it.Horizontal loop systems require a substantially large surface area underwhich trenches approximately three or more feet in width and four toeight feet deep need to be excavated to install the loops in a varietyof configurations. Loops fabricated from polyethylene, meant to carry anaqueous solution, must be considerably longer than theircopper/refrigerant counterpart because the fluid they carry is at a muchlower temperature differential relative to the surrounding earth andtheir thermal conductivity is much lower than that of copper. Inaddition, for both copper and polyethylene loops, the surrounding earthis susceptible to being depleted of thermal energy (in the heating mode)and saturated with thermal energy (in the cooling mode). In order forthe average near-loop earth temperature to be constant, and therefore aneffective heat-sink, a loop of sufficient length is required to mitigatethe depletion/saturation problem. This also mandates a minimumseparation between loops. The near-loop depletion/saturation of thermalenergy occurs because the heat capacity of soil, its ability to absorb alarge amount of heat with only a small change in temperature, is not ashigh as some other materials. In addition, this property, known asspecific heat, varies based on soil composition, compaction and moisturecontent. The most effective material to surround the loops for heattransfer would be one that could absorb/release large amounts of thermalenergy with the smallest change in temperature.

Based on the above considerations, there are two major impediments tothe widespread implementation of ground-source geothermal systems,particularly for smaller residential applications. First, theinstallation of vertical, deep, borehole ground loop systems requiresthe use of expensive borehole drilling equipment with costly up-frontcapital expenditures resulting in a long payback period. Second,horizontal loop systems require a relatively large land surface area tobe effective, severely limiting the pool of potential users. Theirinstallation also has the potential to damage surface embellishment suchas lawns and shrubbery, another discouraging factor.

Consequently, a ground-source geothermal system that could mitigate theabove impediments would be desirable from both a cost and aestheticperspective. A hybrid system that employed multiple, shallow, verticalboreholes, on the order of approximately twelve to twenty five feet deepand two to four feet in diameter, capable of being drilled by lessexpensive equipment than the large drilling rigs, would lower initialcapital costs significantly. Such equipment is commonly used today todrill holes for utility and telephone pole installation. In order forthe shallower borehole system to be effective, based on the aboveconsiderations, three implementation characteristics are necessary. Theyare:

-   1. The loop within the borehole cannot be the simple U-shape    configuration with straight vertical segments; currently the    standard method used for deep borehole geothermal systems. A method    of increasing the effective loop contact area with the surrounding    earth in a shallower borehole must be employed.-   2. The loop must be surrounded by, and in thermal contact with,    material of much higher heat retention characteristics than that of    common soil. The heat retention characteristics of soil can vary    widely depending on compaction; on composition, such as clay, sand    or stone; and to a much greater degree based on moisture content. By    surrounding the loop(s) with material of high, constant, heat    retention characteristics, the efficacy and efficiency of the system    is enhanced and made resistant to thermal fluctuation.-   3. The system must be able to be assembled and installed with a    minimum of expensive equipment and personnel costs.

Prior art geothermal disclosures have attempted to improve onrequirement (1) above. U.S. Pat. No. 5,623,986 discloses a heat exchangesystem with a helically wound loop. A major disadvantage of thisimplementation is that only one-half of the subsurface loop is helicallywound while the other uncoiled half is entirely insulated to eliminateintra-loop thermal “short-circuiting” between the two legs of theU-shape loop. The result is that only one-half of the U-loop is usefulin heat transfer, and the additional expense of insulation material andits installation is incurred.

U.S. Pat. No. 5,054,541 discloses a ground coil assembly geothermalsystem designed for shallow depths. The design satisfies requirement (1)above with a helically wound loop which insures a large thermal transfercapability with the surrounding earth. A disadvantage is the possibilityof thermal “short-circuiting” between sections of the loop, which are inclose proximity. Because the entire unit is prefabricated and thereforemust be transported to the installation site, there is a practicallimitation on the borehole depth that can be used.

BRIEF SUMMARY OF THE INVENTION

It is therefore, an object of the present invention to provide aground-source thermal exchange system that can be more widely used basedon the combination of reduced installation cost and the relatively smallground surface-area footprint required.

In accordance with this invention, there is provided a system composedof stackable, geothermal blocks, which can be assembled at theinstallation site. The blocks are either pre-formed containers that canbe filled with material of high thermal capacity or non-containerizedblocks cast from such material. By stacking the blocks, one upon anotherin a relatively shallow borehole, the need for expensive boreholedrilling equipment currently used to drill deep wells is eliminated.Within the blocks, stacked one upon another and aligned, is at least onepair of passageways in the form of a U-shape in which a thermal transferloop is placed; sections of the loop are helically wound to increase thetotal thermal transfer area Multiple U-shape pairs of passageways withinthe stacked blocks, each having a loop, can be used in a single system.Thermal transfer fluid, either a refrigerant or an aqueous solution, iscirculated through the loop, or loops, to provide heating/cooling to anexternal load.

The modular design of the relatively shallow borehole system results ina low cost of installation because the stackable blocks, particularlythose of the containerized design, can be filled at the installationsite. Also, the need for expensive drilling, excavation or otherspecialized equipment and the associated high, skilled labor cost, isnot necessary. At any site, multiple installations of the system can beimplemented and operated independently or connected in series/parallelarrangements.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a perspective view, partly broken away, of an example of apartially assembled modular, stackable, geothermal block system of thecurrent invention.

FIG. 2A is a top view of a container-type stackable, geothermal blockunit, showing two passageways that extend through the block as well as aflush-mounted filler cap which seals the unit.

FIG. 2B is a sectional view of the stackable geothermal block unit ofFIG. 2A.

FIG. 3A is a top view of a terminal, stackable, geothermal block unitshowing two passageways that extend through the block as well as atransverse passageway that joins the two passageways that extend throughthe block to forming a continuous U-shape passageway.

FIG. 3B is a sectional view of the terminal, stackable, geothermal blockunit of FIG. 3A.

FIG. 4A is a perspective view, partly broken away, of a tube, threadedon the distal end, on which the stackable, geothermal block units can beslidably mounted.

FIG. 4B is a perspective view of a threaded cap used to secure theterminal stackable geothermal block unit to the threaded end of the tubeof FIG. 4A.

FIG. 5 is a perspective view, partly broken away, of approximatelyone-half of a helically wound thermal transfer tubing that is placedwithin the tube of FIG. 4A.

FIG. 6 is a perspective view of an example of an assembled, modular,stackable, geothermal block system placed in a subsurface environment.

DETAILED DESCRIPTION OF THE INVENTION

Within the drawings which describe the preferred embodiments of thepresent invention, like parts are identified with the same numerals.

FIG. 1 illustrates the position of the various elements of the modularstackable, geothermal system 1 in relation to each other and as it wouldbe assembled in a subsurface environment. The order of description ofthe elements will closely parallel the sequence of the preferred methodof assembly of the system.

Thermally conductive tubing 16, contains two helically coiled segmentsof equal length separated by centrally located uncoiled section 16 b.Both ends of the tubing, 16 and 16 c, are also uncoiled. One end of thetubing is inserted into the distal, threaded end of a thermallyconductive tube 18 c and drawn through until the coiled section istotally surrounded by the tube 18. As the tubing is drawn through thetube, a thermally conductive grout 22 a is inserted so that any spacebetween the tubing coils and between the tubing and tube are filled. Thesecond half of the tubing is inserted into the distal, threaded end oftube 12 a using the same procedure described for the first half of thetubing. When in place, the U-shape distal end of the tubing passesthrough an aperture 30 located at the distal end of tube 18 and anaperture 26 located at the distal end of tube 12. A cross sectional viewof part of the tube 18 a displays a cross sectional view of thehelically wound tubing 16 a surrounded by the thermal grout 22. Itshould be noted that the above constructive process can be performed atthe location of the installation of the system or preassembled offsite.The terminal, stackable, geothermal unit 24, of which there is only onein a system, serves as the base for all other stackable units. Itsurrounds the U-shape part of the tubing 16 b, protecting it from beingdamaged and encasing it in thermally conductive grout 22 b. The terminalunit is slidably mounted on the distal end of tubes 18 and 12. Atransverse passageway 32 within the terminal unit permits the U-shapeportion of the tubing to be positioned within it. Fastening means 28 and28 a, threaded caps in this embodiment, attach the terminal unit to thetwo tubes and prevent the leakage of the thermal grout 22 a.

The assembled support structure just described including the tubes 18and 12, the embedded helically wound thermal transfer tubing 16, theterminal stackable geothermal unit 24 and fasteners 28 and 28 a, can nowbe inserted into a borehole.

Once positioned in a borehole, blocks of stackable a geothermal unit 10can be slidably lowered so that the two tubes 18 and 12, pass throughthe corresponding passageways in the blocks. The blocks can beconstructed in two ways; either as containers which can be filled withfluids of material of high thermal capacity or cast from such materialinto a solid, non-containerized unit. It is also possible for a materialto be cast within the containers, either at the installation site or atan offsite location. If the block is a container, a fill orifice andflush-mounted cap 20 is provided.

As has been noted, the system can be placed in a borehole. It can alsobe placed within a trench in a generally horizontal position, however,its orientation is not limited to a vertical or horizontal one. Thesystem can also serve in a submarine location where the protection ofthe thermal transfer tubing would be enhanced by the surroundingelements of the system.

FIG. 2A is a top view of the stackable, geothermal block unit 10, aplurality of which would normally be used in the construction of asystem although a system with a single unit is feasible and practicable.In the unit illustrated there are two passageways 34 and 36 that extendfrom one face to, and through, the opposing face. Although one pair ofpassagways is illustrated, multiple pairs of passageways are feasibleand practicable. Each pair of passageways would enclose a separateU-shape thermal transfer loop. The individual loops can then beconnected in a series, parallel or a series/parallel arrangement toprovide the thermal transfer fluid to/from an external load.

The unit can be cast from a material of high thermal capacity. It canalso be formed as a container capable of being filled through asealable, fill aperture 20, with a fluid or substance of high thermalcapacity.

FIG. 2B is a cross sectional view of the stackable geothermal block unit10 of FIG. 2A, which is illustrated as a container-type unit showing thehollow interior space 46.

FIG. 3A is a top view of a terminal, stackable, geothermal block unit24, only one of which would be used in the construction of a system andwould be placed at the distal end thereof. In the unit illustrated thereare two passageways 35 and 37 that extend from one face to, and through,the opposing face. It should be noted that multiple pairs of passagewaysare feasible and practicable. However, the number of passageways in theterminal unit must match the number of similar passageways in thestackable geothermal block units that overlie the terminal unit. Theterminal unit, when assembled as part of the system, encloses theU-shape central portion of the helically wound thermal transfer tubingand contains a transverse passageway 32 through which the tubing can beinserted and surrounded with thermally conductive grout. The unitillustrated is one that is cast from a material of generally highthermal capacity although it could be fabricated in a different mannerto lessen its weight while maintaining its resistance to compression.

FIG. 3B is a cross sectional view of the terminal, stackable block unit24 of FIG. 3A, which is shown as a unit that has been cast from material38, of generally high thermal capacity.

FIG. 4A is a partially broken perspective view of a thermally conductivetube 18. When used in the assembled system, the stackable, geothermalblock units would be slidably mounted on the tube using thecorresponding passageway of each unit. Part of a helically coiledthermal transfer tubing would be placed within the tube, along with heatconducting grout, so that the U-shape central portion of the tubingwould extend through aperture 30 on the threaded, distal end of thetube. The generally uncoiled proximal end of the tubing would extend outof the proximal end of the tube. It should be noted that a system withmultiple pairs of tubes is feasible and practicable. A system with justone tube can be constructed but it would be much less efficient than asystem with multiple tubes.

FIG. 4B is a perspective view of a threaded cap 28 used to keep thestackable, geothermal blocks that are slidably mounted on the thermallyconductive tube from moving relative to the tube. It also seals thebottom of the tube to prevent the loss of heat conducting grout.

FIG. 5 is a partially broken, perspective view of approximately one-halfof a helically wound thermal transfer tubing 16. The coiled portion ofthe tubing would be placed within a thermally conductive tube along withheat conducting grout. The tubing serves as a conduit for a thermaltransfer fluid, generally either an aqueous solution or refrigerant, toeffect an exchange of thermal energy with an external load. Illustratedare two optional couplings 40 and 42. To facilitate the placement of thesystem in a borehole or trench, it might be expedient to cut theproximal ends of the tubing a short distance from the system and then toreattach the tubing once the system was completely assembled belowground. In this instance coupling 40 would be necessary if the tubingwere fabricated from copper. If the tubing were fabricated from amaterial like polyethylene, a coupling could be used but heat fusionwelding could also be applied, making the coupling unnecessary. Coupling42 would normally be unnecessary, however, in the installation of adirect exchange (DX) system, a refrigerant is used as the thermaltransfer fluid and would exist in both a liquid and vapor state withinthe copper tubing. Therefore, in a DX system, it might be advantageousto have two sections of copper tubing of different diameters. Coupling42 could then be used to attach tubing of two different sizes (notshown).

FIG. 6 is a perspective view of an example of a modular, stackable,geothermal block system 1 that has been placed in a borehole. Shown arethe terminal geothermal unit 24 with six overlying stackable, geothermalheat exchange units 10. The proximal ends of thermally conductive tubes18 and 12 are shown. Extending from the tubes are the proximal ends ofhelically wound thermal transfer tubing 16 and 16 c. Tube couplings 40and 44 are optional and would be used to if the tubing was cut toexpedite the subsurface placement of the system. Tubing 48, extendingfrom coupling 40, to the heating/cooling load would normally beinsulated (not shown) in order to prevent thermal “short-circuiting” tothe surrounding subsurface environment.

The preceding description, given by way of example in order to enableone of ordinary skill in the art to practice the claimed invention, isnot to be construed as limiting the scope of the invention, which isdefined by the claims of the current invention.

1. A stackable geothermal heat exchange unit comprising: a hollow,fillable container having opposed faces, at least one continuouspassageway extending from one face of the container to and through theopposing face, and no permanently integrated thermal transfer fluidtubing; wherein the opposed faces and at least one continuous passagewayof the fillable container define a sealed space; wherein said unit is acomponent of a geothermal heat exchange system; wherein said container,when stacked with other stackable geothermal heat exchange units in ageothermal system can be oriented in a manner such that said continuouspassageways of each unit form an extended, multi-unit continuouspassageways through the full depth of the multiple unit structure; andwherein a cylindrical conduit of non-corrosive material passes throughthe at least one continuous passageway.
 2. The stackable geothermal heatexchange unit according to claim 1 wherein: said unit is formed by acasting process.
 3. The stackable geothermal heat exchange unitaccording to claim 1 wherein: said unit is filled with a fluid.
 4. Thestackable geothermal heat exchange unit according to claim 1 wherein:said unit is filled with a non-fluid material.
 5. The stackablegeothermal heat exchange unit according to claim 1 wherein: the at leastone continuous passageway comprises multiple, paired passageways, thefirst passageway of each pair of continuous passageways serves as aconduit for a thermal exchange supply means, and the second passagewayof each pair of continuous passageways serves as a conduit for a thermalexchange return means.
 6. The stackable geothermal heat exchange unitaccording to claim 5 wherein: said unit is formed by a casting process.7. The stackable geothermal heat exchange unit according to claim 5wherein: said unit is filled with a fluid.
 8. The stackable geothermalheat exchange unit according to claim 5 wherein: said unit is filledwith a non-fluid material.
 9. A geothermal heat exchange systemcomprised of a plurality of stackable geothermal heat exchange unitsstacked upon one another, wherein: said units each comprise: a hollow,fillable container having opposed faces, at least one continuouspassageway extending from one face of the unit to and through theopposing face, and no permanently integrated thermal transfer fluidtubing; wherein the opposed faces and at least one continuous passagewayof the fillable container define a sealed space; wherein said units,when stacked with other stackable geothermal heat exchange units in ageothermal system, are oriented in a manner such that said at least onecontinuous passageway of each unit form at least one multi-unit,continuous passageway extending through all stackable geothermal heatexchange units; and a cylindrical conduit of non-corrosive materialpasses through the at least one multi-unit, continuous passageway. 10.The geothermal heat exchange system according to claim 9, wherein: ahelically would thermal transfer tubing is placed inside the cylindricalconduit.
 11. The geothermal heat exchange system according to claim 10,wherein: the at least one continuous passageway comprises multiple,paired passageways, and said helically wound thermal transfer tubing insaid conduit is joined at the distal ends to form a U-shaped loop. 12.The geothermal heat exchange system according to claim 11, comprising: aterminal, stackable geothermal heat exchange unit comprising: at leastone pair of continuous passageways extending from one face to andthrough an opposing face, and a continuous, transverse passagewayjoining said paired continuous passageways; said terminal, stackableunit is located at the distal end of said stack of geothermal heatexchange units; and said U-shaped loop is protected by the terminal unitfrom external contact.
 13. The geothermal heat exchange system accordingto claim 12, wherein: the stack of units is placed in a borehole. 14.The geothermal heat exchange system according to claim 12, wherein: thestack of units is placed in an excavated trench.
 15. The geothermal heatexchange system according to claim 12, wherein: the stack of units isplaced in a body of water.
 16. The geothermal heat exchange systemaccording to claim 12, wherein: the system is utilized for the directand indirect heating and cooling of structures.
 17. The geothermal heatexchange system according to claim 12, wherein: the system is utilizedfor the production of electrical and mechanical power.